ESPE Abstracts

Background: There are few reports on age-related differences in urinary iodine concentrations, which reflect iodine intake.

Objective: We investigated the relationship between age-related differences in urinary iodine concentration and thyroid function.

Methods: The subjects were 749 children aged 1 year, 677 children aged 3 years (excluding 2 children aged 3 years whose urinary iodine concentration was less than sensitive), 559 children aged 6 years, 348 children aged 7 years, 211 children aged 8 years, 183 children aged 9 years and 26 children aged 10 years who participated in a cohort study at our hospital. Urinary iodine levels were measured, and age-specific values and changes were examined.

Results: The median (range) of urinary iodine (μg/L) at each age was 414 (25-79000) at age 1, 262 (25-6400) at age 3, 243 (29-22200) at age 6, 269 (40-11330) at age 7, 212 (49-25690) at age 8, 221 (29-46300) at age 9, 253. 5(96-2776) at age 10, with 3-10 year old age group being more than adequate according to WHO criteria and 1 year old being excessive. The quartile ranges of urinary iodine (μg/L) were 205-1150 at age 1, 160-498 at age 3, 142-471 at age 6, 158-496 at age 7, 145-390 at age 8, 138-477 at age 9, and 150-434 at age 10, respectively. Of the subjects whose urinary iodine was measured, the number of the subjects who also underwent blood tests showed TSH >5 μIU/ml was 13 at age 1, 12 at age 3, 2 at age 6, 2 at age 7, 4 at age 8, 1 at age 9, and 0 at age 10, but FT4 was within normal range in all cases, regardless of whether TSH was elevated or not.

Conclusion: Since most iodine is metabolized and excreted in urine, urinary iodine is a good indicator of iodine intake. This study suggests that Japanese children have excessive iodine intake, especially in infancy, and that there is no evidence of abnormal thyroid function in spite of high urinary iodine levels in all age groups.